The Multispectral Scanners (MSSs) were the first multispectral sensors to
monitor Earth's resources from space. Developed by Santa Barbara Research Center for
NASA's Goddard Space Flight Center, the first MSS was carried aboard the Earth Resources
Technology Satellite (ERTS 1), subsequently renamed Landsat 1. Five MSS sensors have been
flown, and the sensors on Landsats 4 and 5 are currently operational. The instrument
operates by repeatedly scanning a 24-element fiber-optic array from west to east across
Earth's surface; the orbital motion of the spacecraft provides a natural north-to-south
scanning motion. Then, a separate binary-number array for each spectral band is generated.
Each number corresponds to the amount of energy reflected into that band from a specific
ground location. In the ground-processing system, the binary number arrays are either
directly interpreted by image-classification software or reconstructed into images. The
MSS ushered in an era of hitherto unimagined synoptic knowledge of Earth. An extraordinary
number of uses for MSS data emerged as data were acquired and disseminated: land-use
planning, vegetation inventories, crop growth and health assessments, and cartography, to
name a few. The MSS was an experimental system that exceeded its designers' most
optimistic expectations, not only in the quality of data obtained, but also in the large
user community that developed.